The colonization of grape bunch trash by microorganisms for the biocontrol of botrytis cinerea as influenced by temperature and humidity

Six commercial biocontrol agents (BCAs: Aureobasidium pullulans, Bacillus amyloliquefaciens, B. amyloliquefaciens plantarum, B. subtilis, Metschnikowia fructicola, or Trichoderma atroviride) were applied to bunch trash that was then incubated at one of five temperatures (T, 15, 20, 25, 30, and 35◦ C) and one of five relative humidity levels (RH, 60, 80, 90, 95, and 100%). After 1 to 13 days of incubation (BCA colonization period), the number of colony forming units (CFUs) was assessed. The colonization of bunch trash in response to T/RH conditions and BCA colonization period differed among the BCAs; the coefficients of variation among the BCAs ranged from 104.6 to 397.7%. Equations were developed that accounted for the combined effects of the T, RH, and BCA colonization period on BCA colonization of bunch trash. Assuming that the equations, which had an R2 > 0.87, correctly predict BCA growth under field conditions, they would help farmers select the BCA to be used for a specific application based on weather conditions at the time of treatment and in the following days. The equations would also help predict how long an early season BCA application remains effective and thereby help farmers decide whether and when a second BCA application may be needed.